ALIMENTARY CANAL. 361 



{Viperidae) converted into a canal open at both ends. The teeth 

 appear to be continually replaced. 



Labial glands are present in a row in the upper and lower jaw. 

 The posterior labial gland of the upper jaw is in the poisonous 

 snakes modified as the poison gland. It is larger than the rest 

 and different in structure, and its duct opens into the mouth, 

 sometimes at the base of the poison fang {Viperidae). Sublin- 

 gual glands in the floor of the mouth are also present. 



The tongue is long, narrow and forked, and retractile into a 

 basal sheath. It is well provided with sense organs and is 

 exceedingly protractile. It is used as a tactile organ, and can be 

 protruded through an indentation at the extremity of the snout 

 even when the mouth is closed ; eustachian tubes and tym- 

 panic cavities are absent. The glottis is placed far forwards, 

 close behind or even perforating the tongue-sheath, and can be 

 projected into the mouth during the act of swallowing. The 

 oesophagus is long and leads into the tubular stomach,tlie anterior 

 part of which is dilated, the posterior (pyloric) narrow and 

 intestine-like. Tlie windings of the small intestine are con- 

 nected together by connective tissue and enclosed in a common 

 sheath of peritoneum. The rectum varies in length and 

 there may be a caecum on the anterior part of it. The hver is 

 elongated and not divided into lobes : it extends from the 

 pericardium to the cardiac region of the stomacli. The gall- 

 bladder is placed at some distance from it, on the right side of 

 the duodenum. The pancreas lies on the right side of the 

 duodenum, into which it opens by one or more ducts close to 

 or in common with the bileduct. The spleen is usually distin- 

 guished by its light colour and is placed near the pancreas. 



The cloaca is without a urinary bladder. The anus is placed 

 at the junction of the body and tail, which varies in length in the 

 different families. 



Fat-bodies are present in the form of lobed structiues on each 

 side of the intestine in the hinder part of the body-cavity. 



Thymus and thyroid are present, and the suprarenal bodies 

 have the form of narrow elongated bodies of a yellow colour 

 placed on the renal veins or on the vena cava inferior. 



The glottis is a longitudinal slit and is without distinct epi- 

 glottis, though there may be a trace of the latter. The larynx 

 consists of two lateral longitudinal cartilages connected ventrally 



